Development of a drilling process with torque stabilization

Variation in cutting torque often occurs while drilling a deep hole or a workpiece of composite stiffness. Torque variation is closely related to the rise in frictional torque between the swarf and the workpiece as a hole becomes deeper, and to the change in material property in a laminated composite workpiece. Torque variation degrades the efficiency and stability of the drilling process. This study seeks to eliminate large torque variation during drilling by making the cutting torque constant through an active control method. Approximate dynamic modeling of the drilling torque is proposed, and an adaptive PI control algorithm is applied to regulate torque variation. Numerical simulations and experiments on torque-controlled drilling processes are carried out. Results show that torque stabilization and machining time reduction can be achieved by active control. Experimental results validate the dynamic model and control algorithm.